gravity sewage line 1

[Artisi]

Probably an over simple question for the plumbers in here but I need some clarification on any rule of thumb or thoughts on what is a reasonable length of straight run of 4" dia. PVC at 2% slope from a toilet pan to a septic tank, that is assuming there is a maximum length.
Thanks

 

[PEDARRIN2]

There really isn't a rule of thumb for maximum length - it all depends on the particulars of the installation.

You will have two issues;

1. Final invert at the septic tank.
2. Solids settling out in the pipe.

With a long run, you will have a deeper pipe connection on the septic tank the farther you run the pipe. Septic tanks have to be pumped - and sometimes maintained - so the deeper it is - the harder it will be to maintain.

The longer your run - the more likely solids will settle out before they reach the septic tank. Having a lot of fixtures that flow water without appreciable solids (showers, mop basins, etc.) help push the solids down the line. Extra water closets discharging to the line also help.

A 2% slope will cause the solids to travel farther on less water - but will also cause the final pipe invert to be twice as deep as the standard 1% slope allowed for 4" pipe.

Code (at least the IPC) require cleanouts every 100 feet to help push the solids along if they start clogging the pipe.

I have seen runs as long as 1000 feet - but there were other fixtures discharging water into it, the final invert allowed for it, and there were a good quantity of cleanouts.

 

[Artisi]

Thanks for the precise and useful information - a * for you.