I did a brew yesterday testing out my take on DaaB's False Bottom Mash Tun. There is no significant dead space in this design. I got 80% efficiency.
Very easy to construct:
1) Drill holes in the plate (mine is from a 1970's cake container lid, acryllic?)
2) Cut a hole in the base of the mash tun for the tap
3) Cut some of the thread off the tap such that most of the nut gets a grip and the plate can't touch it
4) Make a few drain channels in the nut, finish off with a flame to remove plastic burrs
5) Figure out some sort of stand so you can get a tube out and reach under to turn the tap, I "reconfigured" an old wooden draw but a couple of bricks would do - needs to support the edge of the tun as supporting the flexible base could raise the plate edge and ruin the filter.
photos: mash tun, stand and plate and water butt tap
I've been using "Waddington & Duval" water butt taps on my boiler and mash tuns for many brews. They don't come loose, crack or otherwise leak, plus all the hozelock stuff fits.
Mash tun with tap underneath
Mash tun with tap underneath
I brew therefore I ... I .... forget