The ornamental design for a filtrationsystem, as shown and described.
FIG. 1 is a front perspective view of a filtration system;
FIG. 2 is a back perspective view of the filtration system;
FIG. 3 is a top view of the filtration system;
FIG. 4 is a bottom view of the filtration system;
FIG. 5 is a first side view of the filtration system;
FIG. 6 is a second side view of the filtration system;
FIG. 7 is a front view of the filtration system; and,
FIG. 8 is a back view of the filtration system.
The broken line showing of a filtration system is included for the purpose of illustrating portions of the article and forms no part of the claimed design.