New connection to existing underground pvc drain pipe

[old_guy]

We have a 3" pvc waste pipe going to our septic tank.  I wish to connect another line to this pipe from a guest house.  The line is buried.

I can dig up and expose a section of the existing pipe, but don't know the best way to make this connection.  The existing pipe will not move, so I cannot simply glue in a Y connection using normal PVC fittings.  Are the rubber slip connectors appropriate for this? 

If necessary I could (big job) dig up the line all the way from the new connection to the tank.  Can the existing pipe move in and out of the concrete tank so I could use glued fittings?

Thanks

[JRR]

You could use PVC unions, about $50 each.  Or you could use PVC couplings ... the kind that don't have the locating ring inside, about $5 each.

[JRR]

..or your could use rubber connections if your codes allow.  I try to avoid them.

[JRR]

Looks like the proper term is "repair coupling" .. and the price is about $10.

[old_guy]

Thank you for your help, JRR.  Now I need to find out what is available at my local plumbing supply.

- John

[JRR]

I hope it helps.  I've become very fond of using unions in drainage and water supply piping.  Yes, its a bit costly and requires extra planning and installation labor.  But unions can make future repairs and reworks much easier.  Just imagine how the drain pipe under a kitchen or bathroom sink can be an easily removable "manifold" if a few unions are included.  No cutting required.  A blessing as your muscles get older.

[Don_P]

I think they are called a "hubless" coupling as well... having had to find one after getting busted for a rubber coupling. Have 2 pairs of hands and work FAST.

[JRR]

True enough about the need for speed.  Another tip, have a visible target that will give you comforting knowledge that you have somewhat centered the coupling across the joint.  Not some target that the coupling will need to touch, but a measured distance target.  I use a Sharpie mark on the pipe 2" away from the desired location of coupling edge.  2" is far enough away to avoid the cleaner, primer and glue operation: but close enough that I can quickly "eyeball/estimate" during the heat of the moment.

I also believe that a lot of glue is better than a thin coating.  Seems to give a bit more time for assembly.

(With unions, there are different problems but usually not this speed challenge.)

[old_guy]

Great info, guys.  Thanks.  Dug over 700 feet of trench with a ditch witch a couple of weeks back.  About 100' of it was for this drain pipe.  A couple of hours was spent with pick and shovel to expose the original pipe with adequate working room.  Will be setting it within a week.

Would have been a much bigger struggle without your help.