My husband changed out our bathroom sink upstairs. It drains into the floor as the plumbing was probably put in during the 1940's. The new sink does not have a overflow hole in it and ever since he switched it out, the bowl fills up quickly and drains very very slowly. What can we do? Please help!

I would disassemble the trap and drain pipe to make sure no debris, rag or junk dropped down the pipe. If nothing is found then put a bucket below the sink to catch water and dump a bucket of water into the sink, does it drain faster?

Sounds like you haven an venting problem. If it drains into the floor then you have a unvented "S" trap and if the bowl has no overflow it sounds like a "vessel sink" that has its own venting problem. Hubby set up a double whammy. Vessel sinks reguire a special, "grid drain",(see image) to be properly vented so they drain correctly. Did hubby install such a drain? Let me know, Tom