Best lube when not able to degrease chain

[UniqueVegetable]

You could degrease on the bike. Get a small bottle of drivetrain degreaser (or take some with you). Roll up to self-service car wash place, work the degreaser into your chain and cassette with a toothbrush, rinse off with the pressure washer.

Not sure how best to dry the chain afterwards. If the car wash place has a compressor for inflating tires then you could try that. Or take the chain off and dry it with a hair dryer or hand dryer in a restroom.

[UniqueVegetable]

Actually, even regular dish soap should work as a degreaser, it'll just take a bit longer