Myself and my partner tried out MessySupplies' Vivi slime extreme.
(Guar gum and Borax solution)
We used 3 packs and got thoroughly coated in it, as the finale ending of a very messy few days.

She's showered off and had no visible mess on her when she left, but now she feels it on her skin a few hours after.

Any advice?
( The only other stuff used was thick MS gunge, but this never produced a phantom sensation even the day after)

Scrub each other with decent quality shower gel. We find all powder gunge leaves a residue that needs to be scrubbed off, unlike food which just washes off in hosedown.

Take a shower together this time coat each other with soap and shampoo and check in to see how each of you are doing for aftercare.

Turns out it was actual phantom sensations; we were fully clean after showing off and later on she would sometimes feel the wet slime rolling and gliding across parts of her skin like she was still in the pool with me.
(she genuinely enjoyed herself so the sensations just relived the fun memories)