3" or 4" PVC pipe for septic

Hopefully within a year ( [img]/forums/images/icons/smile.gif[/img] ) I will have a Morton building built. I'm considering putting in running water plus a toilet so I won't have to run into the house if I'm all dirty working in the outbuilding. My question is should I use 3" or 4" PVC pipe from the Morton to the septic tank? Throughout the house I have 3" PVC but when it exits the house to go to the septic tank the plumber used 4". I will "tee" into the main 4" PVC prior to it reaching the septic tank. Any pros or cons using either one? Is it code that you have to have 4" under ground? By the way I reside in Maryland. Thanks in advance. Stanley

For the insignificant cost increase why consider 3 inch and take more risk?

Pat

[img]/forums/images/icons/tongue.gif[/img] This is a case where bigger may not be better. It is a question of velocity. Will you have sufficient flow to move the solids in a large diameter pipe? Don't forget, sewer piping is considered open channel flow and the flowline is halfway up on the pipe. Pay close attention to slope and use a diameter which will flow at sufficient depth to carry solids. [img]/forums/images/icons/crazy.gif[/img]

"Pay close attention to slope and use a diameter which will flow at sufficient depth to carry solids."

He said 2 inch doesn't cut it, 3 inch is so so and 4 inch is a GOOD size.

[img]/forums/images/icons/smile.gif[/img] Pat [img]/forums/images/icons/smile.gif[/img]

<font color="brown"> If there isn't room for 4 inch you may have to go with 3".
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<font color="purple"> I ran into that recently installing drain lines for down spouts on my pole building.
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I agree with CJDave and suggest speaking to a septic design guy as to the ID and pitch etc.. Also, you do not want to tee into the line, you must Y into it. Maryland is very much into codes, so doing it right the first time is best.

Gary
QualityWater Associates