I am not sure about the grey to white but I don't think it is a good idea. Anyway, what I normally do with usual success:

1) Fit all pipes before prime. Priming softens the PVC so you do not want to disturb the pipe after priming.
2) Prime both parts. I found that waiting to glue is not necessary.
3) Glue both parts. I apply glue on the male side first and then the female side but I do not redip the applicator so as not to get a lot of glue on the female piece.
4) Insert pipe but do not turn more than 1/4 turn.
5) Do not stress too much before 15 min. and pressure test after 2 hours.


Good luck