Flying J normally has dump stations, $10 IIRC.
Check www.sanidumps.com for local dump sites.
Your gray water should be able to be dumped into a sewer drain. I bought a clear sewer cap with a garden hose fitting on it to do that if needed, about $6-7 on Amazon.
If your relatives have an accessible sewer cleanout access, you may be able to dump black water there.
I bought a maceator pump for my TT. It's like a 12VDC sewage version of a garbage disposal. You place it on the TT sewer outlet and it pumps via a 3/4" garden hose. I've read where some actually run the garden hose into an interior house toilet. As of a couple days ago, on sale for $200 at Camping World.
And I read the relative/friend driveway camping is called mooch docking, vice no hookups boondocking
😉
2019 Wolf Pup 16 BHS Limited, axle flipped
2019 F150 4x4 SCrew SB STX 5.0 3.55 factory tow package, 7000#GVWR, 1990 CC Tow mirrors, ITBC, SumoSprings,