I've run my tandem pump dry with no problems. Since the SLS and the steering pump use different fluids they obviously do not share any chambers. Though i do not know exactly how the tandem pump is constructed, I believe you can simply remove the lines to/from the pump and let it drain and not worry about power steering fluid leaking out.

__________________

85 190E 2.3(SOLD)
86 230E (-->300D) sold
87 300D (-->300TD) sold
68 250S w/ a 615 and manual tranny (RIP)
87 300TD (SOLD)
95 S280 "The KRAKEN" (Turbo 2.9 602 transplant) traded
86 190E 2.3... current project