bus garage

[David Anderson]

I am finally going to build something I've always wanted, a bus garage and woodshop combination.  It will be 30x48 purlin and tubing frame with R panel for siding, sliding doors, etc.  I want to put a restroom in it and of course the appropriate RV dump.  (We won't let the code guy know about that.  It will just be an appropriately placed cleanout).

Anyway, I have a problem.  The building placement is such that I have to have a 152' sewer line run from the toilet to the city sewer tap.  To do this I have to raise the pad by 4' from the current grade.  This will take about 450 CY of fill, and this will only get me a 1% pitch (1/8" to the foot) to the tap.   The building inspector said he will allow it with 4" pipe and 3 evenly spaced cleanouts throughout the run.  He really wanted me to use 6" pipe, but I kind of balked at that idea.   I googled "sewer line slope" and found some entities will allow 1% absolute minimum is some special applications, but it is discouraged.   A six inch pipe can pitch as shallow as .84%.

I cannot raise the pad anymore as it will put my floor grade above the top of a 6' fence at the rear of my lot, so four feet is as high as  I can go.   This is a pretty tough lot to build this on, but that's what I have to work with.

Any opinions from you who have plumbing experience?  I appreciate your wisdom.

David

[niles500]

Use a lift pump w/ small tank -HTH

[JackConrad]

Residential lift station?  Jack

[Tom Y]

They use a lot of grinder pumps around here. A 2 foot round tank, 8 feet long with a grinder and switch. When it fills it pumps into a 2 inch line. I would stay away from 6 inch, as I would think it will build up in it with no drop.  Good luck   Tom Y

[dparker]

i have used many of the small residential lift pumps -- they work really well -- as indicated all you will need is a 2" line and you can use any grade you want as it will pump into the sewer tap.  the only concern that i would have would be how you dump your tank -- on my coach i have 165 gal grey/black tank i believe that i could easily overwhelm the pump that i have in the units that i have installed -- they only hold maybe 35 gallons -- two ways to allievate this situation -- dump slow at a rate similar to the capacity of the pump -- I cannot remember exactly but i believe the ones i used did like 15 gals a min. or use a concrete septic tank (most are 1,000 gals) and install your own grinder pump -- materials would be in the 2,000.00 range if you installed yourself -- most likely cheaper than raising your pad and drive 4' --

[Hartley]

I use a lift station system with no problems.

The RV inlet pipe flange is tied to the lift station tank where a 125 volt 1/2 horse lift pump is located. That can pump 5,300 gph through a 2 inch pipe to the septic tank.

I have never been able to overflow it even by dumping a 120 gallon tank to the lift station through a 3 inch rv hose. These things empty so fast that it would take a really big load to back one up. I pump 150 feet uphill too..

The cost for the lift station is about $700 and the 2 inch pipe about $100.

You can get a higher capacity pump also.

[David Anderson]

I use a lift station system with no problems.

The cost for the lift station is about $700 and the 2 inch pipe about $100.

You can get a higher capacity pump also.

Hmmmm, a lift station = $700 and I can get this fill material for $1275.  The kicker is that I want to build a house on this lot in the future, and with a lift station will really discourage a future sale (when I go fulltime in the bus, yeah right).  Anyway, I need to find a plumber who has had experience using a 1% slope on a drain.  If he says, "don't do it," then it won't work.

David

[HighTechRedneck]

Just my opinion, but any buyer that accepted the presence of a 30x48 shop, probably wouldn't see the lift pump system as a negative.

Keep in mind that adding that much fill will require a lot of ground work labor and equipment.  And if not done really well, could lead to substantial cracking of the slab.

[Hobie]

I vote for the grinder/pump.   Keep in mind that the pipe will settle in time and with such a shallow slope you run the risk of a low spot or puddle.   And with solids in the pipe...   

[zubzub]

No reason a macerater lift pump should cost more than $500.  I would not suggest the type which requires a sump pit etc...I have heard of too many problems with this.  In residential applications I use a home unit that cant lift 5' ( I think) self contained unit, any way 2" pipe and off you go.  Many plumbers know squat about this but of course will act like they do.  If you do the larger sump pit, flaot trigger etc.. installation, get a contract with one, get a service plan and a guarentee with all possible provisions accounted for, as these units are ugly and nasty to service and if they don't have to, a plumber will not service this for free.

[HighTechRedneck]

Another factor to consider if you pursue the 1% slope approach:  Be sure to make it clear during planning that technically there is only a toilet (and handsink?) on the line.  Sure you may occasionally dump your bus waste tanks, but how often will that really be?  A shallow slope design may be relying on water intensive drainage (i.e. clothes washer/tub/shower) to wash down the solids.  Without a substantial flow, a 1% slope will likely be prone to "dam building".

[David Anderson]

A shallow slope design may be relying on water intensive drainage (i.e. clothes washer/tub/shower) to wash down the solids.  Without a substantial flow, a 1% slope will likely be prone to "dam building".

I agree with you about that and have that fear, so let's study the lift system in more detail.

If I set the building at the current grade and put a toilet that drops to a holding tank and throw the switch to engage the pump it will pump the waste about 155' up about 3" in elevation gain from the current grade to the city sewer.  Since the city main is 3" higher than my holding tank, what is to keep it from backflowing from the sewer main to the tank which has a lower static level? 

Should I design a system that pumps up to a point higher than the sewer, then over the (hump) and down flow to the main, like an upside down P trap?   I'm picturing in my mind that the holding tank is close to the toilet so I can push the waste up the line.  However, when I see municipal lift stations they are at the lowest point of a gravity fed pipe then the waste is lifted or "forced main" to a high point where it gravity flows again.  This design would require the tank at the end of the pipe which would be lots of digging and appropriate grades, etc. 

From the posts above it seems you guys just take from the near the source and force it up the pipe to the appropriate waste stream.

David

[zubzub]

If I read your post correctly, you have it right.  The lift is on the shortest run possible then gravity takes it to city drain.  So depending on your layout you might end up with a pipe above the frost line ( I did not check your location so this may be mute).  If you want well ( pun?) informed info on this, register at breaktime which is the construction forum of Finehomebuilding (taunton press).  There are a bunch of people there who know way too much about this.  And re: the long 1% grade they will probably redirect you to a plumber's forum, can't remember the name right now.  Anyhow it's do-able and watch out for plumbers who say they know all about this, some do, some don't. 

[niles500]

The lift station should be located at your property/ROW line - lift pumps are not force mains - tank is set to a the depth of your service line at the property line and lifted to traverse (via gravity) the ROW to the municipal gravity main - 150 gal concrete tank should suffice - HTH

[David Anderson]

The lift station should be located at your property/ROW line - lift pumps are not force mains - tank is set to a the depth of your service line at the property line and lifted to traverse (via gravity) the ROW to the municipal gravity main - 150 gal concrete tank should suffice - HTH

That really complicates things.  That means since the property is higher where the main is the tank will have to be set below subgrade to get the appropriate slope which will by my estimate put the tank about 6' deep.  Sheesh, this is gettin very unattractive to do.  I may have a lot that is not worth building on.

David