Resp. Prem Ji,
As per Toilet Vastu, toilet should be located in west or northwest direction. Avoid construction of toilet at the centre and in the east, northeast of the house. The toilet seat should be placed in such a way that the person sitting could face the North or the South. Now a day toilet combined with bathroom is becoming popular due to lack of space. Combined bathroom and toilet should be in north-west direction. It should not be adjacent to Pooja Room, kitchen and under the stairs.
For more deatiled answer please read the article "Vastu for Bathroom and Toilet" from GharExpert.com