The design consists of features of the shape, configuration and ornamentation of the Strainer Tub as shown in the drawings in which:Fig. 1 is a top, side and front perspective view of a strainer tub showing the new design;Fig. 2 is s bottom, side and rear perspective view thereof;Fig. 3 is s top plan view thereof;Fig. 4 is a bottom plan view thereof;Fig. 5 is a front elevation view, the rear elevation being identical thereto;Fig. 6 is a right side elevation view, the left side being identical thereto;Fig. 7 is a cross-sectional view along line 7-7 of Fig. 4; andFig. 8 is a cross-sectional view along line 8-8 of Fig. 4.Drawings of the design are included.