I hated using a baby bath - we stopped using it really soon.
I would have recomended your laundry sink but then you mentioned the kitty litter.
When I wasn't using the laundry tub I used to just use the big bath with just shallow water up to around ear height or just take them into the shower with me and get DH to come and dry the baby while I finished up in the shower.
If I'm in a hurry to get us all clean I still use the shower - its a bit of an adventure sharing a shower with 2 toddlers rofl.