We mentioned last weekend that the ferry Issaquah would leave the Fauntleroy-Vashon-Southworth run this weekend for “fuel-tank cleaning.” Didn’t know till tonight (official Washington State Ferries news release here) that the cleaning is to prep it for the latest biodiesel test starting Monday. Two other ferries are set to try biodiesel starting this spring, including the Tillikum, which also is currently on the Fauntleroy run. The “triangle route” was also involved in a biodiesel test in 2004, suspended because of fuel-filter trouble. (That test involved 20% biodiesel; this new one involves a 5% mix.)