6 yr. Old Dog Soiling Floor

He may have never been completely housetrained.  The change to a new family and now to a new apartment could also have him somewhat anxious which accounts for some housetraining accidents.  I would start crating him when you can't actively watch him.  Take him out frequently and be sure and go with him (you probably do if you're in an apartment).  Praise him and give him a treat when he goes potty outside.  Clean any areas inside where he's soiled or pottied with an enzymatic cleaner.  Don't scold him if he has an accident as this could create anxiety and he may start soiling in hidden areas to avoid your displeasure.  Feed him on a regular schedule and notice when he needs to go and be sure and take him out at those times in addition to other times of day. He may not know how to tell you he has to go out to eliminate so watch him to see if he's signaling in ways you've possibly missed.  Some people teach their dogs to ring a bell hung on the door to alert the owners that the dog needs to go outside. I've never tried this myself because my dogs would be ringing the bell constantly just to go out to romp in the yard. :) Last, be sure he doesn't have some medical issue by taking him to the vet, if you haven't already, for a complete checkup and mention the house soiling to the vet.

Welcome to the forum. :)  I do think if you're consistent and patient you can teach him to eliminate outside only. He's lucky to have found a loving home with someone willing to care for him properly.

What Jackie said!

As others said, he may not have been fully house-trained before. I swear by crate training; it's the quickest way I've ever gotten dogs house-trained.

When my Pom was about a year old, we moved to a new house. She had been fully house-trained up to that point, but once we moved, she started having accidents. A lot. We chalked it up to it being a new environment that she didn't feel very secure in. The biggest problem was at night - she refused to go anywhere she couldn't see us. We started going outside and staying there until she went potty. Would you believe, she refused to go anywhere more than 1-2 feet beyond the patio when it was dark out? Again, we chalked it up to fear- new environment, didn't want to go anywhere unlit or without us. There were times it took just sitting on the patio for 20 minutes until she finally walked a foot into the grass and went.

Your dog may need you to take him out more often, spend as much time as he needs to go, and have a command for it. My dog already knew the phrase "go potty" so when we moved, we made sure that we told her to "go potty" and praised her when she did. It took a while, but it worked.

Good luck and congrats on the new member of the family!

A vet visit to make sure there are no urinary problems?

 I was also going to suggest a vet visit.  If the dog was so poorly cared for, it may well have a UTI.  You can catch a urine sample (first of the morning is best) and take that in.  Easiest way is to use a clean empty yogurt container, tape it to a yard stick. 

 Once health issues are ruled out, work on training.  Training a sick dog is only going to panic the pup.

 Oh UNneutered male.  Is he peeing in the house, or is he marking?  If he is marking, use a belly band, it will save your furniture, carpets and sanity!