[SDguy]

I need to clean out my Hammerhead closed loop pump. I do not want to dismount it, and I especially do not want to open it up. I'd like to just pump vinegar through it in a loop using a small pump.

What I'd like to do is close the true union valves (I have one on the outlet and inlet). Then I'd like to disconnect the union closest to the pump for each valve. So once disconnected, each pump fitting will simply have a half a union hanging off it. Then just attach fittings to these half unions, to a bucket/pump with vinegar.

Here's my question:

Can I connect any half union to the half already in place? Are the unions standardized in their threads?

In other words, will the half union (sch 80) attached to the pump connect properly to a random matching half union purchased at HD (sch 40)?