Plumbing Vents

Repair help for the do-it-yourselfer.
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Tue Nov 11, 2008 1:15 pm

I live in a 1960's mobile home.

Occasionally our toilet would back up into the bathtub or just overflow. The tub and kitchen sink drains have been running slow for the last year or so. The problems always seemed to correct themselves after some plunging, but would come back in a couple months.

A few days ago the toilet overflowed and backed up into the bathtub. I got on the roof and ran water down the 2 vent pipes above the bathroom. This shot some leaves and dirt up into the toilet and bathtub, but did not cause them to drain. After a couple hours everything suddenly drained, I assume due to the weight of the water over time.

I bought and have used some enzyme drain cleaner, since I'm a little wary of using anything acidic on such old pipes. Nothing really improved.

Today I decided to check the 3rd vent pipe above the kitchen. I climbed up and started pouring water in. It filled up to the top after about 1/2 gallon. I pushed a broom handle down and encountered a fairly solid spongy mass that took some good pushing to break down. Hopefully not a dead rat or something... :x

Now the sink drains fine, and the tub and toilet appear ok(only time will tell).

Is it possible that the single vent pipe in the kitchen caused problems in the bathroom? Am I in the clear now? Do enzyme drain cleaners do any good?

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Location: Central North Carolina

Tue Nov 11, 2008 5:41 pm

Only time will tell. If that kitchen drain is somehow tied into the others then having better flow in that one could certainly help.

Our modular has a traditional plumbing system in that one large vent (3" I think) is utilized. But each plumbing fixture (showers, faucets, etc.) has its own Studor type vent and I'm sure that really helps.

I'd only use enzymatic cleaners after having a lousy experience. When we bought this home the smaller bathroom had a slow drain in the tub. The plunger in the tub drain had alot of hair and crap around it and wouldn't back out. I went to Lowe's and bought the standard cleaner claimed to be good for all pipe types. Well I found out it isn't for ABS plumbing, which I later found out we have. Didn't do much for the clog either. I had to back that part out with ViseGrips. That cleaner actually melted the plastic, which wouldn't have been a problem, but it did so in one part of the union that made up the trap and started to leak from there. I used it correctly and flushed with a proper amount of water, but it still did the damage. I just cut those areas out and replaced it all. Now I will only use enzymatic cleaners. Later!
Do what you can today, as you might not be here tomorrow!

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Tue Nov 11, 2008 5:41 pm

Hi & welcome. It's possible but I have my doubts. You could run a snake down them to be sure they are open. I would also snake the drain also. Greg
"If I can't fix it, I can screw it up so bad no one else can either."

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Wed Nov 12, 2008 11:21 am

I agree with Greg. The best way to clear drain and drain vent pipes is with a snake.

The vent pipe over the kitchen can effect drains in other rooms. Almost all mobile homes I work on have 1 1/2" vent pipes. You can have up to 4 fixtures (most times) connected to one drain air vent pipe. Each fixture is given a 'fixture unit value'. This number represents the amount of drainage needed for the fixture. A bath vanity sink is a 1. Most other fixtures, kitchen sink, shower, bath tubs and low flow toilets are a 2. The old non-low flow toilets are a 4. The number of fixture units that can be connected to one 1 1/2" vent pipe is 8, maximum per pipe. I find most manufacturers do not max out this allowance, but some do. So, if you have a semi solid soft but possibly furring thing in the vent, it will certainly lower the amount of air flow through the air vent pipe.

It seems that the mobile home manufacturers are moving towards using the Air Admittance valves (the air valves under the sink). When these are used, at least one standard air drain pipe through the roof must be included in that drain section. These air admittance valves must be accessible under a sink, in a protected wall opening or placed behind a louvered vent on the wall (bad plan).

Hope this helps.
Today is PERFECT!

All information and advice given is for entertainment and informational purposes only. The person doing the work is solely responsible to insure that their work complies with their local building code and OSHA safety regulations.


Wed Nov 12, 2008 12:20 pm

Thank you all for the help.

I will be purchasing a snake today at HD in case the problems start to come up again.

So far so good though. Things are draining nicely.


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Location: Central Virginia

Wed Nov 12, 2008 10:41 pm

Are you on a septic system? It almost sounds like a full septic tank.


Sun Nov 16, 2008 3:50 am

check the pitch of your sewer line.