Personally, I prefer using a combination of Healers, giants, wizards and Valkyries as a leeching army. I add 2 babies to direct the queen to create a proper funnel to the centre of the base.
Depending on the size of your army, use: 4 healers for TH8/9, 5 for TH 10/11/12 (these amounts I used as fixed) 7-11 Giants 8-13 Wizards 1-2 Babies 6-8 Valks 6 wall breakers (I have always kept it fixed @ 6, as you mostly need 3 to break a single wall, and kept 3 at hand in case they ran on a bomb or so) 2-4 archers to clear undefended buildings @ the end The spells can depend on personal preference, but at least take 1 jump (to jump to the centre) and 2 rage (QW support).
1) Use the healers to Queen Walk / charge the outer skirts of the base, keep 2 rage at hand for her. to boost her attack and the healers to push her health back up. Use wall breakers if needed. 2) use the giants to clear any outer defences left, use wall breakers if needed. Then drop wizards to back them and to create the funnel to the centre. 3) Drop a jump spell on walls preventing you from getting to the Centre, then drop your Valks to hit it. I personally use 3 Rage, 1 jump, 2 Freeze, 1 Poison and keep 1-2 Freeze in my CC as emergency back-up. Obviously, these are to prevent the (single) infernos and Eagle Artillery. On TH8-9 you do not require the Freeze, as you will not face many infernos and certainly seldom Eagles :)
It may take a bit of practice, but I have learned it is a very usefull leaching army for all resources, especially DE. The costs of the Valk are earned by the consistent hit you get on the TH and DE storage typically located in the centre of the base. I have not had any base design in which you could not jump to the core using this strategy, unless I messed it up myself.