John Davies wrote:

5) People suggest various vacuum break systems - some say drill small
hole just above check valve, others suggest adding T outside with
riser - do I need the latter?

Install a check valve at the pump discharge outlet, as another poster
suggested, Make sure the valve is readily accessible in case you need
to remove it for cleaning. Important!!! - install a reducing tee and a
small ball valve above the check valve so you can drain the discharge
pipe for winterizatioon and servicing.

The real purpose of a vacuum breaker is to protect your potable water
system. I don't see any reason you would have any need for one on a
sump pump.

I think he is referring to the outlet, one might want a way to break the
vacuum, when the pump is off, so that the pipe will drain, which could
be important if it is subject to freezing.

This is where you would put in a "Y" or "T" fitting, at the top end of
the drain run, so that it will drain on its own. Probably un-needed in a
low use situation, and you would have to be careful of that the pipe
doesn't plug downstream, since that would overflow.

So that is a mixed bag, with good and bad.