The design is the visual features of the SOAP BASKET as shown in solid lines in the drawings, whether those features are features of one of shape, configuration, ornament or pattern or are a combination of any of these features. The portions shown in stippled lines do not form part of the design.Drawings of the design are included.In the drawings:Fig. 1 is a front and left side perspective view of a SOAP BASKET in accordance with said Industrial Design;Fig. 2 is a top plan view of the SOAP BASKET shown in Fig. 1;Fig. 3 is a front elevational view of the SOAP BASKET shown in Fig. 1;Fig. 4 is a bottom plan view of the SOAP BASKET shown in Fig. 1;Fig. 5 is a rear elevational view of the SOAP BASKET shown in Fig. 1;Fig. 6 is a left side elevational view of the SOAP BASKET shown in Fig. 1; and,Fig. 7 is a right side elevational view of the SOAP BASKET shown in Fig. 1.