Originally Posted by Glynn
Put 3 gals of water in your tun and measure what you get back with out tipping the tuns, if you get back 2.5 gals then your dead space is .5 gal. I personally don't measure dead space when i do my mash i tilt the tun to extract all that i can and then batch sparge with 175 degree water to reach 7 gal of total wort. after a 60 min boil I'm usually at or just under 5.5 gal
This is exactly how i do it too. With my system, i have about 4 gallons of sparge water sitting between 172-178 degrees. I batch sparge so ill usually have some left in the mash tun but ill have collected 6.5 to 7 gallons pre boil. I hit around 80% efficiency according to the online calculators i use.
Also, the "weak" tasting beer could be that your crush may be to blame or just not enough grain to start with.