It's there, from the outer valve stem, move 180 degrees to the other side of the rim, then look through that hole and you will see the inner valve stem hiden back there!!
The only way I've been able to check and fill that valve is to roll the MH until that outer valve stem is at an 8 or 9 o'clock position. Then reach behind or in front of the wheel, place your hand between the inner and outer tire and you will feel the valve stem. From this position you can check and inflate the tire!
From everything I've read and talking with Les Schwab they recommend not using a valve extenders on those 22 inch inner tires!
Hope this helps!!!i