You get more HP by doing normal washing with 80 int gear (2 AP per level for no net loss of MP) than by double washing (5 AP per level, 2 resets each).
For max base HP, you need to wash about 17000 extra HP, or 326 AP. If you are wearing INT gear on levelup from level 50, that means 80-90 INT gear per level. If you're wearing it from level 100, you need 130 INT gear or so. That's disregarding previously gained MP, which would help a little.
Max HB'd hp is way easier, you'd only need 20 int from level 50 to do it, which would be anyone who bought their Zakum Helm.
The only reason to double wash is if you have enough AP left (before 200) but can't get the MP necessary to wash out all your points from HP.
For max base HP, you need to wash about 17000 extra HP, or 326 AP. If you are wearing INT gear on levelup from level 50, that means 80-90 INT gear per level. If you're wearing it from level 100, you need 130 INT gear or so. That's disregarding previously gained MP, which would help a little.
Max HB'd hp is way easier, you'd only need 20 int from level 50 to do it, which would be anyone who bought their Zakum Helm.
The only reason to double wash is if you have enough AP left (before 200) but can't get the MP necessary to wash out all your points from HP.