How Do We Purify Filthy Grout in Between Smooth Tiles?

Answered by Ustadh Tabraze Azam
Question: As salamu alaikum.
In Sh. Faraz Khan’s commentary of Ascent to Felicity, he mentions when cleaning an impurity, when you  purify smooth tiles by wiping, the grout in between is not purified merely by wiping because it is rough and not smooth. 
Given this, my question is: in a case of multiple tiles with grout (which may even be chipped in addition to being rough) in between having visible impurity on them, is it sufficient to use foaming cleaning agents and then a towel to wipe the foam and impurity away to make those areas purified? Or if not, how may it be done?
JazakAllahu khair
Answer: Wa alaikum assalam wa rahmatullahi wa barakatuh,
I pray that you are in the best of health and faith, insha’Allah.
(1) Wipe away any obvious filth,
(2) Wash the affected area by pouring water over it, and then soaking it up with a clean cloth until it is no longer dripping wet. This is considered one washing.
(3) Repeat step (2) three times
Thereafter, the area is considered purified as long as there are no apparent traces of filth (color or smell). And any difficult to remove traces are excused.
And Allah alone gives success.
wassalam,
Tabraze Azam
Checked & Approved by Faraz Rabbani