Why delay the lower basin?

The upper 3/9/11 shelves still need their landing rows; early basin pieces occupy the cells needed to reduce those counters.

Which outlet is reserved for the ending?

Keep the right outlet clear for the final green receiver after the four top feeds quiet.

Sand Blocks level guide

expert 7 colors

Level 289 reduces shelves 3, 11, and 9 before loading the basin left-to-right, reserving its upper-right footprint for the final green 2x2.

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Place orange 1x2 at r3c1-r3c2 and yellow corner at r3c3-r4c4; leave cyan lane c6 and row r5c1-r5c6 empty.
Move green L into r2-r3,c5-c6 and cyan 1x2 to r3c4-r3c5; confirm counter 3 changes 3→2→1.
Clear red 1x2 at r5c1-r5c2 and blue horizontal at r5c3-r5c4; wait for shelf 11 to descend to 7 before touching rows 6-10.
Feed yellow to r5c2-r5c4 and cyan to r5c5-r5c6, reducing 11→5 and 9→6; keep basin c5-c6 empty.
At counters 1 and 2, move purple 2x3 into r6-r8,c1-c2 and red 1x2 to r6c3-r6c4; do not cross c4.
Place blue horizontal at r9c1-r9c3 and yellow corner at r9c4-r10c5, then cyan vertical at c4,r7-r9; keep c6 open.
After shelves show 0, place green 2x2 at r6-r7,c5-c6, clear red at r10c1-r10c2, and wait for every receiver to show 100%.

Colors in this level:

Orange, Yellow, Green, Cyan, Purple, Red, Blue

Placing the long purple rectangle in the lower basin before the shelves open.
Closing the top cyan lane while the 3 counter still has sand.
Using the right outlet for a non-green receiver and losing the final green path.

Board notes 5 details

Layout: Four top tubes feed a compact upper grid; shutters marked 3, 9, and 11 descend above a wide lower basin holding green, blue, purple, red, yellow, and cyan receivers.
Goal: Drain the four top colors in order, reduce the upper shelves, and keep the lower basin mostly open until the counters are nearly exhausted.
Opening: Collect orange and yellow under the first tubes, move cyan and green into upper side lanes, and preserve the horizontal row beneath the 9 shelf.
Danger Zone: The long purple rectangle in the lower basin blocks the right green outlet if placed early; closing the cyan top lane before the 3 shelf drains strands the final flow.
Mechanics: Four simultaneous feeds, three descending counter shelves, and a delayed large-basin finish with the last green stream are evidenced.

Why delay the lower basin?
The upper 3/9/11 shelves still need their landing rows; early basin pieces occupy the cells needed to reduce those counters.
Which outlet is reserved for the ending?
Keep the right outlet clear for the final green receiver after the four top feeds quiet.