10 gallons of his tank water which he vacuumed some of his substrate and he shook out on of his filters in it.What are you starting off of a friends?
To get your fish in the water safe fill your tank which you did let it run a day with some aeration.
Next put a fish or fishes in the tank then get your buddies filter and put it on your tank along with your own filter. Let his bacteria seed into your filter.
Very important to not put friends filter on the tank BEFORE fish are in tank.
The tank ran on ~110 gallons of tap water with prime for 2 days before i poured the water from his in. The pleco went in right after i dumped the 10 gallons into my tank. Later that night i added 10 more gallons of tap water with prime. Then the next day i did a 30 gallon water change.