Connecting to sanitary

Can the 2" drain line from a shower tie into the side of a horizontal sanitary line or does it have to tie into the top?

The shower can tie into a horizontal waste line, but it needs to be vented before it does.
Otherwise anything coming down the line can siphon the trap.

If you have only a lav run with 2" pipe on that line, and that is vented, then it would be "wet vented".
Most plumbers have those run in 1.5", so the waste to the lave would need to be pulled and upsized.

JeffreyLB said:

Can the 2" drain line from a shower tie into the side of a horizontal sanitary line or does it have to tie into the top?

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The shower drain line will be vented before connecting to the sanitary.
Thanks

In that case, it's a wye fitting on the horizontal.

If your question is asked correctly, then you cannot use a sanitary tee in a horizontal line, period.