Im running underground wiring from my house about 8 feet to an 18 foot round 48 inches deep to pool pump using GFCI on outside of house and Twist lock outlet 6 feet from pool.
Can I use UF wire run through schedule 40 conduit or do I need to use THWN single conductors through conduit?

It needs to be individual conductors, Romex in conduit will not get rid of the heat.
Why Twistlock? It may get tripped on and expose conductors.

The Town requires twist-lock for filter.