Oh dear, he does not look good at all. You have been given some great advice and you need to act quickly before it is too late. Seems like this health condition has been going downhill for a while due to his emaciated state. Vicky asked about the
UVB light you bought, please give the detailed info of that as it is extremely important. You also need to get a digital thermometer with a long wire & probe right away. If you have a 60 or 75 watt household lightbulb on hand, you should put that in right away so he can somewhat warm up to hopefully help him a little.
Since he is so frail and lethargic, the only way you should be giving him a
bath is by holding him in the palm of your hand with his vent area (where he poos) right down in some warm water as his chances of drowning are very strong.
Were you able to get him to a vet? If not, that is about the only chance he has of survival at this point, have to be honest.